/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.view.groovy;

import groovy.text.Template;
import groovy.text.markup.MarkupTemplateEngine;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextException;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.servlet.view.AbstractTemplateView;
import org.springframework.web.util.NestedServletException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedWriter;
import java.io.IOException;
import java.util.Locale;
import java.util.Map;

/**
 * An {@link AbstractTemplateView} subclass based on Groovy XML/XHTML markup templates.
 *
 * <p>Spring's Groovy Markup Template support requires Groovy 2.3.1 and higher.
 *
 * @author Brian Clozel
 * @author Rossen Stoyanchev
 * @see GroovyMarkupViewResolver
 * @see GroovyMarkupConfigurer
 * @see <a href="http://groovy-lang.org/templating.html#_the_markuptemplateengine">
 * Groovy Markup Template engine documentation</a>
 * @since 4.1
 */
public class GroovyMarkupView extends AbstractTemplateView {

    @Nullable
    private MarkupTemplateEngine engine;


    /**
     * Set the MarkupTemplateEngine to use in this view.
     * <p>If not set, the engine is auto-detected by looking up a single
     * {@link GroovyMarkupConfig} bean in the web application context and using
     * it to obtain the configured {@code MarkupTemplateEngine} instance.
     *
     * @see GroovyMarkupConfig
     */
    public void setTemplateEngine(MarkupTemplateEngine engine) {
        this.engine = engine;
    }

    /**
     * Invoked at startup.
     * If no {@link #setTemplateEngine(MarkupTemplateEngine) templateEngine} has
     * been manually set, this method looks up a {@link GroovyMarkupConfig} bean
     * by type and uses it to obtain the Groovy Markup template engine.
     *
     * @see GroovyMarkupConfig
     * @see #setTemplateEngine(groovy.text.markup.MarkupTemplateEngine)
     */
    @Override
    protected void initApplicationContext(ApplicationContext context) {
        super.initApplicationContext();
        if (this.engine == null) {
            setTemplateEngine(autodetectMarkupTemplateEngine());
        }
    }

    /**
     * Autodetect a MarkupTemplateEngine via the ApplicationContext.
     * Called if a MarkupTemplateEngine has not been manually configured.
     */
    protected MarkupTemplateEngine autodetectMarkupTemplateEngine() throws BeansException {
        try {
            return BeanFactoryUtils.beanOfTypeIncludingAncestors(obtainApplicationContext(),
                    GroovyMarkupConfig.class, true, false).getTemplateEngine();
        } catch (NoSuchBeanDefinitionException ex) {
            throw new ApplicationContextException("Expected a single GroovyMarkupConfig bean in the current " +
                    "Servlet web application context or the parent root context: GroovyMarkupConfigurer is " +
                    "the usual implementation. This bean may have any name.", ex);
        }
    }


    @Override
    public boolean checkResource(Locale locale) throws Exception {
        Assert.state(this.engine != null, "No MarkupTemplateEngine set");
        try {
            this.engine.resolveTemplate(getUrl());
        } catch (IOException ex) {
            return false;
        }
        return true;
    }

    @Override
    protected void renderMergedTemplateModel(Map<String, Object> model,
                                             HttpServletRequest request, HttpServletResponse response) throws Exception {

        String url = getUrl();
        Assert.state(url != null, "'url' not set");

        Template template = getTemplate(url);
        template.make(model).writeTo(new BufferedWriter(response.getWriter()));
    }

    /**
     * Return a template compiled by the configured Groovy Markup template engine
     * for the given view URL.
     */
    protected Template getTemplate(String viewUrl) throws Exception {
        Assert.state(this.engine != null, "No MarkupTemplateEngine set");
        try {
            return this.engine.createTemplateByPath(viewUrl);
        } catch (ClassNotFoundException ex) {
            Throwable cause = (ex.getCause() != null ? ex.getCause() : ex);
            throw new NestedServletException(
                    "Could not find class while rendering Groovy Markup view with name '" +
                            getUrl() + "': " + ex.getMessage() + "'", cause);
        }
    }

}
